Role of complement in innate immunity and host defense.

The complement system is an important part of the innate immune defense. Next to its role as an effector mechanism of the innate immune system, complement also plays a major role in shaping the adaptive immune response. The complement system is also involved in several other physiological processes such as tissue regeneration and clearance of immune complexes and dead cells. Unfortunately complement is also involved in pathology by contributing to tissue damage, induction of autoimmune reactions and chronic inflammation. Tight regulation of complement activation by both fluid-phase and membrane bound complement inhibitors is essential to maintain a good balance between optimal protection with as little as possible damage to the host. Alterations in this balance and hence the function of complement, by influence of auto-antibodies, or genetic variants, may render the complement system into a harmful player in tissue damage and pathology.